docs: def formfield_for_foreignkey(self, db_field, request=None, **kwargs):
          """
          Replicates the logic in ModelAdmin.forfield_for_foreignkey, replacing
          the widget with the patched one above, initialising it with the child
          admin site.
          """
          db = kwargs.get('using')
          if db_field.name in self.raw_id_fields:
              kwargs['widget'] = PolymorphicForeignKeyRawIdWidget(
                  db_field.rel,
                  admin_site=self._get_child_admin_site(db_field.rel),
                  using=db
              )
              if 'queryset' not in kwargs:
                  queryset = self.get_field_queryset(db, db_field, request)
                  if queryset is not None:
                      kwargs['queryset'] = queryset
              return db_field.formfield(**kwargs)
          return super(PolymorphicAdminRawIdFix, self).formfield_for_foreignkey(
              db_field, request=request, **kwargs)